Melatonin decreases cocaine-induced locomotor activity in pinealectomized rats

Objective: Several studies have shown that the time of day regulates the reinforcing effects of cocaine. Additionally, melatonin and its MT1 and MT2 receptors have been found to participate in modulation of the reinforcing effects of such addictive drugs as cocaine. Loss of the diurnal variation in cocaine-induced locomotor sensitization and cocaine-induced place preference has been identified in pinealectomized mice. In addition, several studies in rodents have shown that administration of melatonin decreased the reinforcing effects of cocaine. The objective of this study was to evaluate the effect of melatonin on cocaine-induced locomotor activity in pinealectomized rats at different times of day (zeitgeber time [ZT]4, ZT10, ZT16, and ZT22). Methods: Naïve, pinealectomized Wistar rats received cocaine at different times of day. Melatonin was administered 30 min before cocaine; luzindole was administered 15 min prior to melatonin and 45 min before cocaine. After administration of each treatment, locomotor activity for each animal was recorded for a total of 30 min. Pinealectomy was confirmed at the end of the experiment through melatonin quantitation by ELISA. Results: Cocaine-induced locomotor activity varied according to the time of day. Continuous lighting and pinealectomy increased cocaine-induced locomotor activity. Melatonin administration decreased cocaine-induced locomotor activity in naïve and pinealectomized rats at different times of day. Luzindole blocked the melatonin-induced reduction in cocaine-induced locomotor activity in pinealectomized rats. Conclusion: Given its ability to mitigate various reinforcing effects of cocaine, melatonin could be a useful therapy for cocaine abuse.

Melatonin suppression increases the incidence and progression of chemically induced oral cancer in rats / Supressão de melatonina aumenta a incidência e progressão do câncer de boca induzido quimicamente em ratos

Estudos sugerem que a supressão de melatonina e disfunção circadiana em trabalhadores noturnos podem estar relacionadas ao desenvolvimento e à progressão do câncer. Pesquisas têm mostrado também que a incidência tumoral pode ser aumentada pela pinealectomia. Entretanto, nenhum estudo avaliou a influência da cirurgia de pinealectomia sobre o desenvolvimento e a progressão do câncer de boca. No presente estudo, nós investigamos os efeitos da supressão de melatonina sobre a ocorrência e a progressão tumoral um modelo pré-clínico de câncer de boca induzido quimicamente. Nós demonstramos, pela primeira vez, que ratos pinealectomizados tiveram maior ocorrência de carcinoma espinocelular de boca, comparado aos animais controle. Ratos pinealectomizados também exibiram volume e espessura tumorais cerca de 3 e 2 vezes maior que animais sham, respectivamente. Além disso, pinealectomia induziu atrofia do epitélio não-tumoral adjacente às lesões bucais. Os ratos pinealectomizados apresentaram maior resposta inflamatória no front de invasão tumoral, caracterizada principalmente pelo aumento do número de eosinófilos e macrófagos associados ao tumor. Tumores de ratos submetidos à pinealectomia exibiram maior imunoexpressão de ERK1/2 e p53 no microambiente tumoral. Estes resultados revelam que a supressão de melatonina acelera o desenvolvimento e a progressão do câncer de boca associado ao aumento de eosinófilos e macrófagos no front de invasão tumoral e maior expressão de ERK1/2 e p53 no microambiente tumoral(AU)

Studies suggest that melatonin suppression and circadian dysfunction in shift workers can be related to cancer risk. Furthermore, investigations have shown that pinealectomy promotes higher tumor incidence in rats. However, no study evaluated the influence of pinealectomy surgery on oral cancer onset and progression. In the current study, we investigated the effects of melatonin suppression on tumor occurrence and progression in a preclinical model of oral cancer. We demonstrated for the first time that pinealectomized rats had higher oral squamous cell carcinoma occurrence than sham animals. Furthermore, pinealectomized animals displayed tumor volume and thickness about 3 times and twice higher than sham-operated rats, respectively. Moreover, pinealectomy induced atrophy of non-tumor epithelium adjacent to the oral lesions. Pinealectomized rats showed higher mean number of tumor-associated macrophages and eosinophils in the carcinoma invasion front. In addition, tumors from pinealectomized rats displayed increased immunoexpression of ERK1/2 and p53 in the tumor microenvironment. These results reveal that melatonin suppression promotes higher oral cancer occurrence and progression associated with increasing of inflammatory cells and ERK1/2 and p53 expressions in the tumor microenvironment(AU)